Leaf and canopy scale drivers of genotypic variation in soybean response to elevated carbon dioxide concentration

Abstract

The atmospheric [CO ] in which crops grow today is greater than at any point in their domestication history and represents an opportunity for positive effects on seed yield that can counteract the negative effects of greater heat and drought this century. In order to maximize yields under future atmospheric [CO ], we need to identify and study crop cultivars that respond most favorably to elevated [CO ] and understand the mechanisms contributing to their responsiveness. Soybean (Glycine max Merr.) is a widely grown oilseed crop and shows genetic variation in response to elevated [CO ]. However, few studies have studied the physiological basis for this variation. Here, we examined canopy light interception, photosynthesis, respiration and radiation use efficiency along with yield and yield parameters in two cultivars of soybean (Loda and HS93-4118) previously reported to have similar seed yield at ambient [CO ], but contrasting responses to elevated [CO ]. Seed yield increased by 26% at elevated [CO ] (600 μmol/mol) in the responsive cultivar Loda, but only by 11% in HS93-4118. Canopy light interception and leaf area index were greater in HS93-4118 in ambient [CO ], but increased more in response to elevated [CO ] in Loda. Radiation use efficiency and harvest index were also greater in Loda than HS93-4118 at both ambient and elevated [CO ]. Daily C assimilation was greater at elevated [CO ] in both cultivars, while stomatal conductance was lower. Electron transport capacity was also greater in Loda than HS93-4118, but there was no difference in the response of photosynthetic traits to elevated [CO ] in the two cultivars. Overall, this greater understanding of leaf- and canopy-level photosynthetic traits provides a strong conceptual basis for modeling genotypic variation in response to elevated [CO ].

Photosynthesis in a Changing Global Climate: Scaling Up and Scaling Down in Crops

“…This suggests that breeding programs aiming to improve crop biomass production will also have an effect on photosynthetic physiology (Flood et al, 2011). Supporting this observation, the increase in crop yields detected in plants grown under elevated [CO 2 ] (Ainsworth and Long, 2005;Long et al, 2006;Sanz-Saez et al, 2017;Torralbo et al, 2019) are also associated with higher photosynthetic rates measured under such conditions.…”

“…These parameters can be used to distinguish differences of photosynthetic efficiency under different environments allowing researchers to identify better-adapted cultivars ( Aranjuelo et al, 2009 , 2013 ; Sanz-Saez et al, 2017 ); or be used as input parameters for earth systems models that predict ecosystem responses to environmental changes ( Rogers, 2014 ). However, a lack of information about V cmax and J max in some species in several ecosystems is the major source of error using earth systems models ( Rogers, 2014 ).…”

“…In the future, drought occurrence and severity are projected to rise, increasing the risk of yield loss by 24% in soybean, 21% in maize, 18% in rice, and 20% in wheat (Leng and Hall, 2019). On the other hand, the predicted increase in atmospheric CO 2 levels, as a substrate of photosynthesis, is expected to increase yields by up to 30% depending on plant species and other environmental conditions (Ainsworth and Long, 2005;Long et al, 2006;Sanz-Saez et al, 2017). It has been shown that elevated temperature and drought can negate the positive effects of elevated CO 2 on yield (Ruiz-Vera et al, 2013;Gray et al, 2016).…”

Yield response of field‐grown soybean exposed to heat waves under current and elevated [CO2]

“…Together, the United States, Brazil, and Argentina produce 88% of the world's soybean that is utilized for livestock feed, vegetable oil, biodiesel, and direct human consumption (FAO, ). In the Midwestern United States, the sensitivity to changes in [CO 2 ] varies across soybean cultivars, but field studies at elevated [CO 2 ] consistently show photosynthesis ( A N ), water‐use efficiency (WUE), and yield all increase (Ainsworth & Long, ; Bernacchi, Kimball, Quarles, Long, & Ort, ; Bernacchi et al, ; Bishop, Betzelberger, Long, & Ainsworth, ; Leakey et al, ; Sanz‐Sàez et al, ). These benefits, referred to as the “CO 2 fertilization effect,” are threatened by increasing frequency and intensity of heat waves driven by the “CO 2 greenhouse effect” (Ainsworth & Ort, ; Pryor et al, ).…”

Assessing diversity in canopy architecture, photosynthesis, and water‐use efficiency in a cowpea magic population

“…Improvement of photosynthesis has been widely proposed as a key target for increasing crop yield (Simkin et al, 2019;Weber & Bar-Even, 2019;Wu et al, 2019). Evidence of the benefit of increased photosynthetic activity for seed yield is supported by experiments in elevated CO 2 for diverse crops (Ainsworth & Long, 2005) and legumes such as soybean (Morgan, Bollero, Nelson, Dohleman, & Long, 2005;Sanz-Sáez et al, 2017). More studies are needed to determine the effectiveness of breeding for high A canopy and its translation to high yield.…”